1. Field of Invention
The invention relates to telecommunications networks, and more particularly to advanced architectures for telephone networks.
2. Description of Related Art
The incremental, feature by feature extension of the calling features available to users of the telephone network has given rise to the well known feature-interaction problem. As new options are added to the suite of call choices it becomes increasingly difficult to manage the behavioral complexity of the features and their resulting interactions. For instance, a telephone subscriber may subscribe to call waiting, caller ID and 3-way calling features. What happens to that subscriber when a 3-way call is made, then interrupted by a call waiting signal, can be problematic. Redesign of old telephony features to fit smoothly with the range of new features is usually not a practical option. Eventually the resulting patchwork complexity damages the quality and productivity of all phases of telecommunications service and development. It is actually the case that if not for special layers of monitoring software that examine the states of local office switching systems (such as commercially available 5ESS) and compensate for errors, the mean time between failure in those switching systems would be measured in hours, rather than months or years.
The inventors themselves in earlier work have analyzed telephone systems and their burgeoning feature sets in terms of a general decomposition into a connection specification and specifications of each user interface (P. Zave and M. Jackson, xe2x80x9cRequirements for Telecommunications Services: An Attack on Complexityxe2x80x9d, Proceedings of 3rd IEEE International Symposium on Requirements Engineering, IEEE Computer Society Press, pages 106-117, 1997). Each of those specifications aimed to allow for composition of the behavior due to each feature that could be relevant to the specification. That approach proved difficult, the fundamental difficulty lying in the complexity of combining the feature behaviors within each specification, and the difficulty of finding mechanisms that could handle that complexity.
Other approaches in the art trying to manage feature interactions have rested on an architectural foundation, for instance those described in J. M. Duran and J. Visser, xe2x80x9cInternational Standards for Intelligent Networksxe2x80x9d, IEEE Communications XXX(2):34-42, February 1992; J. J. Garrahan, P. A. Russo, K. Kitami and R. Kung, xe2x80x9cIntelligent Network Overviewxe2x80x9d, IEEE Communications XXXI(3):30-36, March 1993; and J. Kamoun, xe2x80x9cFornal Specification and Feature Interaction Detection in the Intelligent Networkxe2x80x9d, Chapter 2, Department of Computer Science, University of Ottawa, Ottawa, Ontario, 1996.
In these approaches the applied architecture is that of the xe2x80x9cIntelligent Networkxe2x80x9d, or something closely related to it, which is a conceptual model oriented towards two-party calls. Features such as conferencing, call multiplexing, call queuing and others which connect or relate more than two parties present serious difficulties for such a conceptual model. Other architecture-based approaches known in the art include those reflected in I. Zibman, C. Woolf, P. O""Reilly, L. Strickland, D. Willis and J. Visser, xe2x80x9cMinimizing Feature Interactions: An Architecture and Processing Model Approachxe2x80x9d in K. E. Cheng and T. Ohta, editors, Feature Interactions in Telecommunication Systems III, IOS Press, Amsterdam, 1995, pages 65-83; M. Weiss and T. Gray, xe2x80x9cExperiences with a Service Environment for Distributed Multimedia Applicationsxe2x80x9d in P. Dini, R. Boutaba, and L. Logrippo, editors, Feature Interactions in Telecommunication Networks IV, IOS Press, Amsterdam, 1997, pages 242-253; W. J. Barr, T. Boyd and Y. Inoue, xe2x80x9cThe TINA Initiativexe2x80x9d, IEEE Coninzunications XXXI(3): 70-76, March 1993; and N. D. Griffith and H. Velthuijsen, xe2x80x9cThe Negotiating Agents Approach to Runtime Feature Interaction Resolutionxe2x80x9d in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 217-235. In the latter known approaches the analytic architecture is more flexible than the Intelligent Network, being based on agents that interact by sending messages to each other as needed. Agents may model users, resources, connections and services; or, more abstractly, may negotiate on behalf of interested parties. In some cases, both styles of representation may be used.
In most of the known approaches call features are not regarded as first-class distinct components in the architecture. That idea however is found in other known approaches, for instance reflected in K. H. Braithwaite and J. M. Atlee, xe2x80x9cTowards Automated Detection of Feature Interactionsxe2x80x9d in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 36-59; and K. P Pomakis and J. M. Atlee, xe2x80x9cReachability Analysis of Feature Interactions: A Progress Reportxe2x80x9d, Proceedings of the International Symposiumi on Software Testing and Analysis, 216-223, January 1996, which characterize a feature as a stacked finite-state machine, in which the stack levels correspond to feature priority.
Other characterizations of telecommunication call features are also known in the art. In T. Ohta and Y. Harada, xe2x80x9cClassification, Detection and Resolution of Service Interactions in Telecommunication Servicesxe2x80x9d in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 60-72; and A. Gammelgaard and J. E. Kristensen, xe2x80x9cInteraction Detection, a Logical Approachxe2x80x9d in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 178-196, a feature is defined as a set of state-transition rules. In J. G. Thistle, R. P. Malhame, H. -H. Hoang, and S. Lafortune, xe2x80x9cFeature Interaction Modelling, Detection and Resolution: A Supervisory Control Approachxe2x80x9d in P. Dini, R. Boutaba, and L. Logrippo, editors, Feature Interactions in Telecommunication Networks IV, IOS Press, Amsterdam, 1997, pages 93-107, a feature is represented as a finite-state machine subject to supervisory control.
In M. Faci and L. Logrippo, xe2x80x9cSpecifying Features and Analyzing Their Interactions in a LOTOS Environmentxe2x80x9d in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 136-151; and K. E. Cheng, xe2x80x9cTowards a Formal Model for Incremental Service Specification and Interaction Management Supportxe2x80x9d in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 152-166, a feature is a process in a process algebra. In J. Blom, B. Jonsson and L. Kempe, xe2x80x9cUsing Temporal Logic for Modular Specification of Telephone Servicesxe2x80x9d in L. G. Bouma and H. Velthuijsen, editors,Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 197-216; and P. Combes and S. Pickin, xe2x80x9cFormialization of a User View of Network and Services for Feature Interaction Detectionxe2x80x9d in L. G. Bouma and H. Velthuijsen, editors, Feature Interaction in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 120-135, a feature is a set of rules in a temporal logic. F. J. Lin and Y. J. Lin, xe2x80x9cA Building Block Approach to Detecting and Resolving Feature Interactionsxe2x80x9d in L. G. Bouma and H. Velthuijsen, editors, Feature Interactions in Telecommunications Systems, IOS Press, Amsterdam, 1994, pages 86-119, also regard features as distinct components to be configured according to architectural constraints.
However, none of the known approaches to network feature management or specification effectively manage the basic feature interaction problem in the telephone network. A systematic approach for telephone network architecture which effectively and reliably manages all the permutations of call features, current and future, is fundamentally desirable.
The invention overcoming these and other problems in the art relates to a telecommunications network system and method which introduces a network technology, distributed feature composition (DFC), enabling efficient and stable telecommunications networks, including those capable of containing the feature-interaction problem. Using the invention, an existing menu of call features can be modified, extended or added to with consistency and much reduced chance of unexpected feature interference and system malfunction. The invention achieves these and other advantages in part by incorporating a virtual architecture for telecommunications systems within which a feature corresponds to a small number of component types, and in which a customer call is handled by building a configuration of components communicating by featureless internal calls through the communications network, connected by the underlying network substrate or architecture.
A desired new feature is specified by describing a small number of new component types, usually just one, along with clear rules for joining the components into configurations.
The architectural style of the invention has something in common with known dynamic pipe-and-filter technologies, in which the filters are the feature components and the pipes are the internal call connections between components. Filters are independent entities, each with its own state, sharing no state with other filters and independent of the identities of its neighbors, as known in the art. This independence contributes significantly to the ability of the invention to manage feature interactions. However, the invention expands on these notions and incorporates a full blown virtual architecture, offering possibilities for convenient mapping to typical physical network architectures.